1. Field of the Invention
The present invention relates to a holding sealing material, an exhaust gas purifying apparatus, and a method for manufacturing an exhaust gas purifying apparatus.
2. Discussion of the Background
Exhaust gas discharged out of an internal combustion engine of a diesel engine or the like contains particulate matter such as soot (hereinafter, sometimes referred to as PM) and in recent years, that PM causes harm on the environments and human being has drawn attention as a big issue. Since exhaust gas further contains harmful gaseous components such as CO, HC, and NOx, the effects of the harmful gaseous components on the environments and human being also have become a serious concern.
Therefore, as an exhaust gas purifying apparatus for collecting PM in exhaust gas or purifying harmful gaseous components, there are proposed various kinds of exhaust gas purifying apparatuses composed of an exhaust gas treating body made of a porous ceramic such as silicon carbide, cordierite, or the like, a casing for housing the exhaust gas treating body, and a holding sealing material including inorganic fibers and provided between the exhaust gas treating body and the casing. This holding sealing material is installed mainly for the purpose of preventing the exhaust gas treating body from contact with the casing covering its circumference and breakage due to the vibrations and impacts generated during the driving of an automobile, or preventing exhaust gas from leaking between the exhaust gas treating body and the casing.
Herein, since an internal combustion engine is to be driven in condition close to the theoretic air/fuel ratio in order to improve the fuel performance, the exhaust gas tends to become at high temperature and high pressure. When the exhaust gas at a high temperature and high pressure comes to an exhaust gas purifying apparatus, the distance between an exhaust gas treating body and a casing fluctuates due to the difference of their thermal expansion coefficients. That is, the distance between the exhaust gas treating body and the casing becomes wider at a high temperature than at a low temperature. Therefore, the holding sealing material is required to have enough holding power for the exhaust gas treating body to keep the position of the exhaust gas treating body in spite of some fluctuation of the distance. Further, in order to efficiently extract exhaust gas treatment function of the exhaust gas treating body, a requirement for the holding sealing material having a heat insulating property for keeping the temperature of the exhaust gas treating body has been becoming high.
In order to satisfy these requirements, in recent years, a designing means is employed in which the thickness of a holding sealing material is made thick to heighten the heat insulating property. With respect to such a holding sealing material, in order to assure repulsive force of inorganic fibers from which the holding power is mainly derived, it is necessary to increase the weight per unit surface area of the holding sealing material.
However, as the thickness of the holding sealing material becomes thicker, it becomes more difficult to obtain sufficient peel strength by needling treatment carried out in a production process for increasing the peel strength in the thickness direction, and there occurs a problem that significant shearing deformation or the like of the holding sealing material is caused in the case an exhaust gas treating body wound with the holding sealing material is stuffed in a casing.
On the other hand, it is also proposed to obtain a holding sealing material with an increased weight by combining a plurality of mats with a weight same as that of a conventional one but not by changing the thickness of each holding sealing material. As an example of such a holding sealing material, there is disclosed a holding sealing material obtained by layering a plurality of mats in JP-A 2007-218221.
With respect to a conventional holding sealing material disclosed in JP-A 2007-218221, a plurality of mats are fixed to one another by bundling parts by sewing machining.
The contents of JP-A 2007-218221 are incorporated herein by reference in their entirety.